CAS: Enabling Synthesis through Small Molecule Liberation

With the support of the Chemical Catalysis Program in the Division of Chemistry, Professor Jon Tunge of the University of Kansas is studying the development of strategies that utilize the innate energy in molecules to enable new environmentally sustainable processes for chemical manufacturing. Specifically, the liberation of small stable molecules (carbon dioxide and/or hydrogen) from simple feedstocks, sometimes in combination with harvesting light energy, will provide the energy to drive chemical reactions without the need for traditional, more wasteful, methods of energy input.

To further lessen the environmental impact of the chemical processes being designed, catalysts based on earth-abundant cobalt metal will be utilized as reaction promoters in lieu of traditional expensive noble metals. These new catalysts will also allow the design of new types of reaction pathways. It is anticipated that the methods developed will be applicable to the synthesis of a wide variety of materials with potential applications as pharmaceutical agents, agrochemicals, and other substances of value to science, engineering, and commerce.

The broader impacts of the funded project extend to the benefits accrued to society as Professor Tunge and his coworkers engage in outreach and educational activities designed to integrate the goals of this research with training and recruitment programs that incorporate the promotion of 'green chemistry' principles. A significant goal of these activities will be to engage in outreach to educate area K-12 students on common chemistry that occurs in their everyday environment and to connect these observables to contemporary challenges in sustainable chemistry.

A further goal is to utilize these community connections to attract students from diverse backgrounds, including individuals belonging to groups underrepresented in STEM (science, technology, engineering and mathematics) fields, to careers that address critical issues of sustainability.

The funded project is focused on the development of chemical transformations based on the catalytic generation of reactive intermediates via the cleavage of C–C and C–H bonds. The catalytic pathways being developed utilize decarboxylation to provide an efficient strategy for the in situ formation of synthetically useful reactive intermediates directly from inexpensive carboxylic acids.

Other processes under investigation utilize the hydrogen evolution reaction for atom-economical functionalization. Cobalt catalysts replace traditional, expensive, palladium catalysts in decarboxylative coupling reactions and are anticipated to allow for new transformation types that are inaccessible using current technologies. Additionally, photoredox-catalyzed hydrogen evolution will allow for the site-specific functionalization of amino acids and peptides, while also enabling regiocontrolled decarboxylative Heck-like acylations and regiochemically complementary allylations.

Performing these new transformations in series will further allow construction of complex molecules through temporally- and kinetically-controlled iterative decarboxylative couplings. The ongoing studies will advance a general paradigm for synthetic chemists to use for accessing reactive species under mild conditions, while generating minimal waste using: (1) visible light photoredox catalysts for redox shuffling of transition metal catalysts, and (2) hydrogen evolution to allow oxidative couplings through liberation of the smallest molecule, hydrogen.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.